Is it off topic to ask how to learn to express oneself in a near fluent manner without visiting a predominantly German-speaking country? I do believe it's possible. Browsing this website daily would be one invaluable resource for doing so.
Asking for an idiomatic expression for writing or talking is one of the finer points we love to see discussed here on German Language.
So, yes, I strongly believe that any such question is on topic as long as it meets other criteria we had defined (e.g. one question - one answer, enough context provided, ideally some own research included, no list-question, not too subjective).